Employee Benefit Plans (Detail) - Schedule of net periodic costs (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Nov. 30, 2012	Nov. 30, 2011	Nov. 30, 2012	Nov. 30, 2011
Pension Plans, Defined Benefit [Member]
Service cost	$ 0	$ 0	$ 0	$ 0
Interest cost	1.7	2.1	3.5	4.2
Expected return on assets	(2.6)	(2.7)	(5.3)	(5.4)
Amortization of (gain) loss	0.5	0.3	1.1	0.7
Net periodic benefit (credit) cost	(0.4)	(0.3)	(0.7)	(0.5)
Other Postretirement Benefit Plans, Defined Benefit [Member]
Service cost	0	0	0	0
Interest cost	0.4	0.5	0.8	0.9
Net amortization of prior service credit	(0.1)	(0.2)	(0.2)	(0.3)
Amortization of (gain) loss	0.9	1.0	1.9	2.1
Net periodic benefit (credit) cost	$ 1.2	$ 1.3	$ 2.5	$ 2.7